1. Field of the Invention
The present invention relates to improvements in the electromechanical battery, and more specifically, it relates to a method for leveling the power output of an electromechanical battery during its discharge.
2. Description of Related Art
Efficient and cost-effective means for storing electrical energy is becoming an increasing need in our electricity-oriented society. For electric utilities an emerging need is for distributed storage systems, that is, energy storage at substations, at solar or wind-power sites, or for load-leveling at the site of major consumers of their electricity. One of the important consequences of distributed storage for the utilities would be the reduction in transmission losses that would result from having a local source of load-leveling power. For the transportation sector the need for energy storage, now acute, is for better batteries to power electric vehicles. These diverse uses are becoming increasingly important as we move toward the use of alternate energy sources.
One answer to the entire spectrum of energy storage needs just outlined is the "electromechanical battery". The E-M battery has the potential to solve both of the above energy storage problems in a manner superior to the electrochemical battery in all important attributes: energy storage density (kWh/kg), power density (kW/kg), energy recovery efficiency, cycle lifetime, and amortized capital cost.
An electromechanical battery is an energy storage module consisting of a high-speed rotor, fabricated from fiber composite, and having an integrally mounted generator/motor. The rotor operates at high speed, in vacuum, inside of a hermetically sealed enclosure, supported by a "magnetic bearing", that is, a bearing that uses magnetic forces to support the rotor against gravity. Magnetic bearings are a virtual necessity for the E-M battery in order to achieve long service life, and to minimize frictional losses so that the battery does not lose its charge (run down) too rapidly. These considerations mitigate against the use of conventional mechanical bearings in the E-M battery for most applications.
The E-M battery has much to contribute in the area of improving the efficiency of both stationary and vehicular systems. For example, many electrical utilities utilize "pumped hydro" energy storage systems as a means of improving the utilization of their "base-load" power plants. That is, electrical energy is stored during off-peak hours for delivery at times of peak usage. These pumped hydro systems employ upper and lower reservoirs, between which water is shuttled to store and recover the energy. Of necessity, pumped hydro storage facilities are located in mountainous areas, usually far, both from the urban centers where power uses are concentrated, and from the sites of the power plants themselves, increasing the transmission line losses that subtract from the useful energy. More importantly, pumped hydro systems themselves only return from 65 to 70 percent of the electrical energy input required to pump the water from the lower reservoir to the upper one. Thus, including the extra transmission losses, of order 40 percent of the input electrical energy is wasted in every cycle of use of the facility. For a (typical) pumped hydro system capable of accepting 5000 Megawatt-hours of input energy, this would represent a direct loss of 2000 Megawatt-hours of electrical energy per diurnal cycle of use.
Contrast the above situation with that offered by the E-M battery. First, banks of such batteries could be used at locations throughout the electrical grid, thereby reducing transmission losses. Second, instead of a 65 to 70 percent "turnaround efficiency", E-M batteries can demonstrate efficiencies in excess of 90 percent. The long-term payback of such an increase of efficiency is obvious: Over a 20-year period (the expected life of a well-designed E-M battery), the energy cost savings from replacing an overall 60 percent efficient 5000 Megawatt-hour storage system with a distributed energy storage system with 90 percent turnaround efficiency is substantial: For a system cycled 300 times in a year, with electrical energy costing, say, $0.05/kwh, the 20-year savings would amount to $450 million. This amount of money is comparable to the original cost of the storage system itself.
The efficiency gains of using the E-M battery instead of conventional electrochemical batteries in an all-electric vehicle are equally dramatic: Ordinary batteries return only 60 to 70 percent of their charging energy input as electrical output. Despite this, by employing so-called "regenerative braking" (putting the kinetic energy recovered from braking back into the batteries), in urban driving cycles, owing to the higher efficiency of its drive train, an electric auto using conventional batteries should require only about 40 percent as much primary energy input as an equivalent-sized gasoline-powered automobile. That is to say, it can be calculated that it would require the energy equivalent of 2.5 barrels of oil delivered to the refinery to equal the urban driving range that one barrel of oil (or its energy equivalent) would give if delivered to the electrical utility to generate the electrical energy to charge up the electric vehicle.
If the same calculation is made, using the E-M battery and its higher turnaround efficiency in the evaluation, a factor of 4.5 to 5.0 is realized, instead of 2.5, that is, a further improvement of nearly a factor of two is predicted. This result would not only mean a near doubling of the urban driving range of the electric auto for the same battery storage capacity, but, more importantly for the nation, it would mean a major reduction in the need for energy for automobile transportation, and with it, a major reduction in the air pollution caused by that sector.
From these examples, it seems clear to that the successful development of the E-M battery could have a major impact on diverse energy-intensive activities of our modern civilization.